The requirements which must be built into a ceramic tile die for forming granular ceramic material into dry pressed tile blanks for ceramic floor and wall tile will be better understood by being aware of the conditions to which such a die is subjected in forming ceramic tile and the type of presses used. All ceramic tile dies in general consist of a case of female member having one or more through openings which form the outer dimensions of the tile to be shaped, a lower punch or male member entering from the bottom of the case and operating vertically with respect to the case, and an upper punch or male member entering the top of the case to compress the ceramic material. Regardless of the press used, the action of the die members must be the same to produce structurally sound tile, free of laminations, or so-called "air blows".
Laminations in ceramic dry-pressed tile are fully explained in U.S. Pat. No. 3,671,618 Huber et al., which clearly defines the die and press action necessary to produce structurally sound tile.
Of three types of presses used in the tile industry, the friction type is the most common; but also, the most abusive for the tile dies. A horizontal fly wheel is mounted on a vertical worm screw threaded through the press crown, with a ram bearing upper punches being attached to the lower end of the worm by a ball joint. Two friction discs driven by a horizontal shaft, one on each side of the fly wheel act to change the fly wheel direction. The case is mounted to rods extending through the stationary press bed and is actuated by an air cylinder from below, and lower punches are secured to the press bed. As a friction disc contacts the fly wheel, the worm drives the ram containing the upper punches downwardly. Just before the punches enter the case, the friction disc is disengaged, and the inertia of the fly wheel drives the upper punches downwardly until the pressure of the punches on the compacted material is sufficient to absorb the energy. As the fly wheel comes to rest, the expansion of the compacted material causes the fly wheel to reverse its rotation. A play in the ball joint allows the worm screw to reverse without lifting the ram, thus allowing the weight of the ram and upper punches to remain on the compacted tile with enough pressure to allow the release of internal stresses, but not permitting the displacement of fractured parts. The air in the cylinder supporting the case permits the case to recede under the pressure stroke as stops on the upper ram come into contact with the case to position the punches at the correct depth in the case. However, there is not enough air pressure to lift the weight of the ram and upper punches, and thus the compressed tile remains sandwiched between the upper and lower punches. Just before the reversed worm screw moves sufficiently to take up the amount of play in the ball joint, a second downward clutching is made reversing the fly wheel rotation for a second impact stroke. As this stroke is completed, the fly wheel is clutched for the return of the ram to rest position.
The above described press cycle imparts a hammer-like blow to the material within the die. When considered these blows represent an impact of around 125 tons or 2,000 PSI on the compact material.
The toggle acting press is probably the fastest acting press of the three types of presses. While its strokes are more of a squeeze than an impact, the increased speed accounts for severe shock to the ceramic tile die. The operation of the toggle acting press is fully described in U.S. Pat. No. 3,523,344 to Huber et al.
Some hydraulic presses are used in the industry, but due to their slower action they are used mostly where high pressures are required, such as around 3,000 PSI. Their action is relatively the same as the friction and toggle presses, but completely controlled by the slower hydraulic action.
Conventionally, ceramic tile die assemblies have been provided with a multiple cavity case constructed of an outer frame with cross members interlocked to this outer frame forming openings equal to the outer dimension of the tile to be formed. With cases having tandum rows, other members extend across the case at right angles to the first cross members and are interlocked thereto. General practice has been to make the parts from hardened and tempered alloy steels to provide the wearing surfaces of the cavity. The alloy steel held up well agains the shock and abuse, but the abrasive ceramic material resulted in a short wear life. Also, the machining, grinding and fitting of these members with the accuracy required to assure that each opening is dimensionally the same is expensive, resulting in high tooling costs.
Methods have been developed to avoid replacing these expensive members when worn by facing the wear portion of the cavity with less expensive removable inserts and replacing them when worn. Many problems arise in attempting to secure these inserts, especially on the cross members, without increasing the width of said members and thereby reducing the number of openings permissable within the die area. Also, problems occur if the means of attaching the insert requires a screw having a head on the wearing side of the insert or that portion within the operating range of the lower punch. With this attachment method, there exists the danger of the screw backing out and binding the action of the lower punch. Additionally, the opening created by the screw head invites the buildup of ceramic material which will pack causing the binding of the lower punch as well as causing undue wear on the face of the insert due to the grinding action of the ceramic material as the lower punch is actuated to eject the pressed tile. Once an alloy steel insert becomes worn, it must be discarded.
Ideally, a material such as cemented tungsten carbide, having a wear resistance many times that of handened alloy steels, should be used in the manufacture of ceramic tile dies. However, the costs of machining the same eliminate the use of this material for the tile die. Tungsten carbide could be employed for tile die inserts, but unfortunately a character of tungsten carbide is that as the hardness and wear resistance is increased, the brittleness increases and shock resistance is lowered. Under the conditions present in a conventional ceramic tile die, tungsten carbide inserts chip or fracture immediately and become worthless.
Tungsten carbide inserts have previously been found to be practically impossible to operatively attach to a case assembly. Braising or silver soldering a tungsten carbide insert to the case members, especially in the lengths required, 41/4 .times. 41/4/ and 6 .times. 6 dies, is not successful due to the difference in expansion of the two metals when heated. Under heated conditions fracturing of the tungsten carbide occurs.
Screw connections for the tungsten carbide inserts present the same problems experienced with other screw connected inserts. In fact, it has been found that the rigid connection in any manner of tungsten carbide inserts to the case assembly results in the chipping or fracture of these inserts during a tile pressing cycle due to the high tensile stresses experienced by the inserts. These seemingly insurmountable problems have tended to discourage the use of cemented tungsten carbide as a material adapted for use in ceramic tile dies.
A primary object of the present invention is to provide a novel and improved case assembly for a ceramic tile die which is adapted to include tungsten carbide inserts to provide die cavity wear surfaces. This is accomplished by providing an insert support assembly which is permitted to move relative to a case assembly frame to relieve shock under extreme conditions which would normally damage the inserts.
Another object of the present invention is to provide a novel and improved case assembly for a ceramic tile die having a novel insert support assembly to support inserts so that at least two wear surfaces thereof may be effectively utilized. The individual inserts are provided with bottom attachments to the insert support assembly so that the side wear surfaces of the inserts are free for use as wear surfaces. This bottom attachment also permits the inserts to be used without increasing the thickness of the die cavity defining structure.
A further object of the present invention is to provide a novel insert structure for use in a ceramic tile die which is universally adapted to be positioned at any location in a die cavity defining assembly to provide a wear surface for the die cavity. This insert structure may be repositioned to provide a minimum of two usable wear surfaces for the die cavity, and all inserts for the ceramic tile die are the same size and shape.
A still further object of this invention is to provide a novel tungsten carbide insert structure for use in a ceramic tile die having a tapered entry edge conforming to the maximum misalignment angle of a tile press to minimize chipping of the insert.